# Anelastic torsional oscillations in Jupiter's metallic hydrogen region

## TL;DR

This paper models anelastic torsional Alfvén waves in Jupiter's metallic hydrogen region, exploring their propagation, reflection, and potential observational signatures to understand Jupiter's internal dynamics and magnetic field.

## Contribution

It introduces a model of anelastic torsional waves in Jupiter's metallic hydrogen region, including their propagation, reflection, and observational implications, extending prior incompressible models.

## Key findings

- Waves travel perpendicular to the rotation axis over several years.
- Reflections at the magnetic tangent cylinder can form standing waves.
- Waves may cause observable variations in Jupiter's rotation and zonal flows.

## Abstract

We consider torsional Alfv\'en waves which may be excited in Jupiter's metallic hydrogen region. These axisymmetric zonal flow fluctuations have previously been examined for incompressible fluids in the context of Earth's liquid iron core. Theoretical models of the deep-seated Jovian dynamo, implementing radial changes of density and electrical conductivity in the equilibrium model, have reproduced its strong, dipolar magnetic field. Analysing such models, we find anelastic torsional waves travelling perpendicular to the rotation axis in the metallic region on timescales of at least several years. Being excited by the more vigorous convection in the outer part of the dynamo region, they can propagate both inwards and outwards. When being reflected at a magnetic tangent cylinder at the transition to the molecular region, they can form standing waves. Identifying such reflections in observational data could determine the depth at which the metallic region effectively begins. Also, this may distinguish Jovian torsional waves from those in Earth's core, where observational evidence has suggested waves mainly travelling outwards from the rotation axis. These waves can transport angular momentum and possibly give rise to variations in Jupiter's rotation period of magnitude no greater than tens of milliseconds. In addition these internal disturbances could give rise to a 10% change over time in the zonal flows at a depth of 3000 km below the surface.